A hallmark of sarcomeric gene mutations in cardiomyopathies is their ability to alter the calcium regulation of cardiac muscle contraction. In general, the Ca2+ sensitivity of contraction decreases in dilated (DCM) cardiomyopathy;whereas, in hypertrophic (HCM) and restrictive (RCM) cardiomyopathies, the sensitivity increases. Since multiple forms of cardiomyopathies exist, the identification of new drugs that sensitize (+) or desensitize (-) the Ca2+ sensitivity could potentially reverse (+ or -) these aberrant changes. Therefore, the goal of this proposal is to use high throughput screening (HTS) to identify small molecules that can modulate the Ca2+ sensitivity of cardiac muscle contraction. To achieve this, we will use a model system composed of cardiac muscle regulated thin filaments (RTF) which are comprised of F-actin, tropomyosin and troponin (Tn). The RTF in combination with myosin (thick filament) make up the major proteins found in the contractile apparatus. In the absence of myosin, the RTF retains all of the Ca2+ regulated functions critical for muscle activation and relaxation. The proposed assay will use cardiac Tn (CTn) complexes that contain fluorescently labeled troponin C (CTnC), the Ca2+ binding subunit of the CTn complex. This will allow us to monitor changes in RTF fluorescence that occurs when Ca2+ binds to the CTnC regulatory site. Therefore, detecting an increase or decrease (+ or -) in the labeled RTF fluorescence intensity at a fixed [Ca2+] and wavelength in response to a compound or "hit" from the HTS screen will indicate that a change (+ or -) in the apparent Ca2+ affinity of CTnC has occurred. Hits from the HTS will be further validated using two biological secondary screens. Based on the above, the RTF system can provide a robust, stable and physiological assay to identify compounds that specifically alter the RTF Ca2+ sensitivity and not the force via cross bridge-drug interactions. To achieve our goals, this proposal will pursue two Specific Aims. Knowledge gained from these studies can uncover potentially new pharmacological agents for the investigation and treatments of cardiomyopathies, hypertension and other forms of cardiovascular diseases. PUBLIC HEALTH RELEVANCE: The genetic basis for three major types of inherited cardiomyopathies including dilated, hypertrophic and restrictive have been studied intently over the last decade. The studies proposed here will identify new low molecular weight compounds, using modern high throughput screening technology, which can modulate a key phenotype that has been observed in model systems of these diseases. Results from these studies will ultimately be beneficial in developing new therapeutic approaches for the treatment of these and potentially other forms of cardiovascular disease.